Process for the conversion of dolomite



3 051 552 PROCESS FOR THE CibNiiERSiON F DOLOMITE Andr Sabl, Marseille, France, assignor to Societe dElectro=Chimie dElectro-Metallnrgie et des Acieries Electriques dUgine, Paris, France, a corporation of France Filed June 30, 1959, Ser. No. 824,082 Claims priority, application France iuly 2, 1958 3 Claims. (Cl. 23-201) This invention relates to the process for the conversion of dolomite.

Certain magnesium-containing brines saturated in NaCl, such as concentrated sea water or water from salt marshes, constituted for the most part of chlorides, may contain as much as 40% of their magnesium content in the form of sulphate and, for that reason, their utilization as a source of magnesium or as an agent in the conversion of slaked dolomite raises, because of this fact, a certain number of problems.

The known processes lead to the production of magnesium hydrate contaminated with calcium sulphate.

The conversion of slaked calcined dolomite according to the equation:

gives residnary brines containing calcium chloride and for a long time attention has been given to utilizing such residuary brines for converting magnesium sulphate into magnesium chloride and eliminating a portion of the sulphate in an insoluble form according to the equation:

By recycling residuary brines according to Equation B, it is theoretically possible to obtain a brine which contains magnesium only in the form of chloride and contains only the 80.; ions corresponding to the solubility of CaSO .2H O in the brine. Now the measurements eflected by applicant have proved that said solubility, for a brine containing neither 30.; nor Ca ions in excess of the stoichiometric formula CaSO is at 20 C. about 0.09 normality, that is:

=7.7 5 grams/liter of.CaSO .2H O

or 2.52 grams per liter of OaO. The MgCl in solution (0.88 normality) in a magnesium brine corresponding, for example, to concentrated sea water contains about 17.6 grams per liter of MgO. Thus, the CaO in solution in the form of CaSO represents i.e., 14 to 15% by weight of the MgO to be extracted.

If, during the conversion according to Equation A, the solubility of gypsum (crystallized CaSO.,.2H O) in the brine remained unchanged, the sulphate concentration remaining unchanged, it would be possible theoretically to avoid the precipitation of 0210 (in the form of sulphate) with the precipitation of the Mg(OH) But this is not the case. Applicants work has shown that as the brine becomes richer in OaCl according to Equation A, the solubility of CaSO .2I-I O decreases by homoionic efiect to a value of 0.012 normality in 80 (therefore in CaSO .2H O) at the end of the operation. Therefore, if all of the Mg in solution, that is, as hereinabove indicated, about 17.6 grams MgO per liter, is precipitated, the corresponding enriching of the brine in CaCl causes a loss of solubility of the 80.; ions from 0.09 to 0.012=0.078 normality, that is, 2.2 grams CaO as sulphate, or 12.5% of the weight of MgO precipitated from the brine. Now

3,051,552 Patented Aug. 28, 1962 ice this CaO content of 12.5% would still render the Mg(OH) unfit for most of its industrial uses.

The curves of FIGURE 1 show the variations of the solubility of CaSO .2H O in the brine considered. The excesses in 80., (shown at the left of the line XY), stated in normalities compared to the formula CaSO .2H O, are represented in .abscissas; the concentrations in CaSo .2H O, also stated in normalities, are represented in ordinates.

The left side of FIGURE 1 corresponds to the transformation of MgSO into MgCl according to Equation B, i.e., by addition of CaCl to the initial brine. 50,, ions are precipitated from the solution as CHSO4.2H2O but the etlect of the decrease in concentration of 80.; ions in the solution resulting from this precipitation is to increase the solubility of the gypsum by decreasing the homoionic eliect SO SO4Ca.2H O.

As shown on the right-hand portion of FIGURE 1, when all of the MgSO .2H O has been transformed, the added CaCl remains in the solution and acts by homoionic eilect Ca++SO Ca.2l-I O. As the concentration in CaCl increases, the gypsum solubility decreases.

In order to limit the CaO precipitating as sulphate with the magnesum hydroxide, it is advantageous, as shown on the right portion of FIGURE 1, to introduce, preferably by partial recycling of the exhausted brines to the initial brines, a strong excess of CaCl which, without precipitating any magnesium, dilutes and gives a brine containing, for example, as much as CaC-l as MgCl (0.44MgC1 +0.44CaCl and wherein the calcium sulphate solubility is only 0.02 normality (point A of the curve). Then the excess of calcium sulphate is eliminated by crystallization of CaSO .2H O

and the liquors are treated so as to precipitate the magnesium. Now, after complete precipitation of the magnesium, the 02150 solubility in the residuary waters lowers to only 0.012 normality (point B). In consequence, the solubility loss is only 0.020.0l2=0.008 normality, that is, 0.225 gram CaO per liter for 8.8 grams precipitable MgO per liter, i.e., a ratio CaO/Mg0=2.5% instead of 12.5 but this, however, is still too high.

Of course, it would be possible to go still further by recycling more brine. However, the curves show that only small gains in CaO precipitated as sulphate per unit of MgO produced may be obtained, and this is at the cost of a substantial decrease in yield per unit of volume of treated brine.

Now, applicant has also found that:

(1) When disposing of a brine rich in CaCl such as described hereinabove, containing, for instance,

normality and saturated in NaCl, if said brine is diluted with water, the CaSO; solubility is strongly increased. For example, for a 1:1 dilution, the solubility becomes 0.058 normality (point C) and, if the magnesium from said diluted brine is precipitated according to Equation A, e.g., up to MgCl =0.04 CaCl =0.40 (point D), the solubility of CaSO is still 0.036 normality, that is much higher than the initial CaSO, content of the brine before dilution, or 0.02 normality before dilution (point A) which, after dilution, has become 0.01 normality. Consequently, the magnesium precipitation may be realized without any risk of contaminating the precipitate by the CaO in the form of CaSO (2) The diluted brines hereinabove described are not suitable for the desulphating. Effectively, the gypsum crystallization must be carried out in a medium concentrated in CaCl and saturated in NaCl if small contents of CaSO, corresponding to point A are desired. But on the other hand, the make-up CaCl may be extracted in concentrated medium from a cycle similar to the one described in Example III of applicants copending application Serial No. 821,399, filed June 19, 1959, entitled Process for the Conversion of Dolomite, now Patent No. 2,033,650. This process consists in soaking and cqunteriiow converting slaked dolomite with a magnesiui-n brine saturated in NaCl. This process is suitable idrbrines free from sulphate, If, as in the present case, the utilized brines contain sulphates, part of the process may nevertheless be used with no risk of contaminating the'Mg(OH) due to the inertia of calcium sulphate molecules in precipitating in this medium as CaSO .2H O c y t ls The present invention concerns a process for the conversion of slaked dolomite by brines containing MgCl saturated in NaCl and comprising, besides chlorides, a noticeable proportion of sulphates, which consists in:

(a) Desulphating these brines by mixing them with concentrated saline solutions from recycling rich in' CaCl without lowering the NaCl content of the mixture, in order to take advantage of the low solubility of calcium sulphate in a' concentrated medium;

(b) Preparing recycling solution by carrying out the first steps of the dolomite conversion into Mg(OH) by MgCl in a concentrated brine and avoiding the contamination of Mg(OH) by calcium sulphate, thanks to the inertia of gypsum in crystallizing in said medium;

' (a) Eliminating the calcium sulphate by precipitation in devices distinct from the converters;

(d) Diluting the desulphated brine; and

(e) Completing the counterflow conversion of dolomite by taking advantage of the fact that the solubility of calcium sulphate increases with dilution and thus avoids contamination of the magnesium hydroxide by calcium were:

The invention consists also, as indicated hereinafter, in combining these diverse operations in one complex cycle comprising at least two circuits, one of which at least utilizes concentrated brine and another one diluted brine, for instance, by incorporating washing water.

The combination of the two processes described hereinabove in (1) and (2) leads etfectively to a complex cycle, wherein the last steps of conversion are realized, as indicated in (e), in diluted medium, preferably by mixing washing waters of the final product with desulphated brine, andwherein the first step, or steps, works as indicated in (b) in concentrated medium.

In these steps, the passage into solution of CaCl from the reaction of MgC1 on the lime from dolomite according to Equation A, as shown on the right portion of the curves of FIGURE 1, lowers the CaSO solubility and the brines, already saturated, in CaSO become supersaturated. But applicant has observed that, in said brines, most charged indeed in various ions but wherein the concentration in 80,, ions is only a few centinormalities, the appearance of the first CaSO .2H O crystals generally requires delays of about one or several hours, while the contact with the'dolomite during the conversion lasts only about a quarter of an hour at the first steps of conversion. However, the CaSO .2H O supersaturated at each passage being eliminated by crystallization, each step utilizedas a source of CaCl in concentrated medium is doubled with a desulphater in which the supersaturated brine is brought into contact with CaSO .2H O nucleus crystals, and this long enough to destroy the supersaturation. The first desulphater is also used for the precipitation, as calcium sulphate, of most of the 80.; ions brought along by the primary brine.

Therefore, the concentrated brine saturated in NaCl circulates in closed circuit in each system: converter, desulphaten but with a very high ratio:

Stay in desulphater Stay in converter whence a very high ratio of desulphater volume to converter volume, about 40:1 for instance. There must be such decanting (or filtering) surfaces that the brines from the desulphaters be not only desupersaturated but also free from fine crystals in suspension.

The concentrated circuit receives the primary brine rich in MgCl and in MgSO and gives desulphated brine, a portion of which is recycled for the desulphating, and the remaining, after dilution by the washing waters, is used -for completing the conversion in the diluted circuit.

Example The complex cycle thus realized will appear more clearly from FIGURE 2, given as'an example, which shows the quantities of liquids and their concentrations (expressed in millinormalities) ofMg, Ca and $0 in the various circuits. The first circuit, the circuit employ ing concentrated brine (concentrated 15mm comprises:

Two desulphaters S and S One soaking vat T One converter .0

The second circuit, the circuit employing diluted brine (diluted circuit), comprises:

Three converters D 13 and D Three washers L L and L The number of these devices can be varied.

We have at our disposal:

First, a source of magnesium brine 2 (concentrated sea water containing Mg as chloride and sulphate) characterized by the following contents:

Mg=850 millinormalities Ca=70 millinormalities SO =350 millinormalities Second, stock of desulphated brines 4 and 6 (prepared synthetically, or obtained by substituting Ca ions for a part of the Mg ions in an appropriate quantity of brine Z and maintained in contact with gypsum crystals long enough to destroy the super-saturation in S0 or obtained from a prior operation) characterized by the following compositions: I

M5 0 m l i m l e Brine 4 Ca=210 millinormalities S04=40 millinormalities Mg.= millinormalities Brine 6 Ca=420 millinormalities SO4=2 5 millinormalities an in uc m at hat h d at n volume 4 and 6 would, respectively, represent 12 and 32 times the hourly input of brine 2, to be used for the conversion of dolomite.

Concentrat ed Circuit into the converterG as indicated by the line 12.

' During this soaking operation, a part of the dolomite was converted according to Equation A, whereby 300 millinormalities of Mg were eleminated from the brine and substituted in the dolomite for an equivalent number of normalities of Ca primarily contained in said dolomite, while 295 millinormalities of Ca passed into the solution as CaCl and are now available for desulphating operations in desulphaters S and S bringing about enough Ca to satisfy Equation B and also an excess capable of starting the insolubilization of 80,; ions by homoionic efh Thus, the whole arrangement, vat T, converter C and desulphaters S and S which forms the concentrated circuit, is temporarily balanced as regards its internal outputs, but it is short in Mg since 450 millinormalities of feet in concentrated medium. 5 Mg have disappeared from the brine to be replaced by The brine transferred from vat T to desulphater S the same amount of Ca ions from dolomite and it shows contains: an excess of Ca since, for 445 millinormalities of Ca M mininormalities passed in solution as CaCl the crystallization as gypsum Ca=505 millinormalifies has respectivelyremovedirom desulphaters S and S S0 :35 mininormalifies 280+25=3Q5 mrlhnormalrties only. The excess is 445 3 05 140 mrllrnormahtres. Thfifefofe, it is largely supersaturated in 4 ions Since, In order to restore the balance between Ca and Mg in such a concentrated brine containing about 0.5 normali coming i d t f th h l tr t d iry of Ca ions, the solubility Of the 4 ions Would be cuit, desulphater S is supplied with one volume of brine y 18 millinormalities. 2, rich in Mg and poor in Ca, and an equivalent volume In spite of said supersaturation, and owing to the short f brine 4, poorer in Mg but richer in Ca than brine 2, Contact duration minutes) in the Vat the Contamiis withdrawn from desulphater S and feed through pipe nation of dolomite by CaSO .2H O is very Sma (5 m l- 21 to converter D (for the feeding of the diluted cirlinormalities). cuit). There is thus obtained:

In converter C, the soaked dolomite, comrng from vat +1vo1umebriue2 Mg=850 Ca: 70 804:350 T, is put in suspension in brme taken from desulphater 1volumebrine4 Mg=400 Ca=210 so4= 40 S and, for 1115 milrliutes, this same brine is continuously mfierencpo +450 +310 Egg t mug pm 6 14 up to a total volume of 2 The dirference between 310 millinormalities of excess Afterwards, the decanting operation is carried out. sulphate in the circuit and 305 millinorrnahtres of The brine which has reacted on dolomite is sent back CaSO .2H O through Plpe desulphater s2 and the Pamany removed in the desulphaters S and S corresponds to 5 vemdfiolwm 1S Pfi COHVerter millinormalities of caso which have contaminated the D urmg hrs operation in converter C, 2(175100) :150 dolomite during the soaking operation P f'Q of Mg dlsappearefi from the two "Q 36 For an output distribution as hereinabove, .the unbal- Of 13171115 uhllzed and were substlthled y an equlvalent ance would thus be rectified as regards the whole concenhumbel' of milhllofmahties initially Present in the trated circuit, butit would not be solved between desuldolomite, while 150 CaCl millinormalities were added haters S and S which would show the following b lto the 295 millinormalities from the preceding soaking an +1 volume Mg=850 Ca= 70 SO =Oinbrine2 +1 volume =175 =420 25 item desulphater S -1 volume =400 =21) 40 to vat T Desulphater S1 1 volume =400 =2l0 40 to converter D; =2s0 =2s0 in CaSO .2H;O

+1 volume Mg=100 Ca=505 SO= 35 from vat T +2 volumes =200 =990 from converter 0 2 volumes =350 =840 50 to converter 0 Desulphater S2 1 volume =175 =420 25 to desulphater S1 0 225 +210 15 operation in order to increase the homoionic efiect of Therefore, to restore the balance, it is necessary to insolubilization of S0 ions in desulphater S complete the moves already considered with an internal As the brine which has reacted in converter C returns circulation between these two brines 4 and 6, giving for to desulphater S it does not leave the concentrated cirone volume of brine exchanged: cuit. Its composition is: 90 Mgzwo 08:21) 804510 Mg=100 millinormalities =42, =25 Ca=495 rnillinormalities 50,:25 millinormalities Dlfiergmes ,;33; ,3

Therefore, is is also supersaturated in S0,; ions since, 5 On the whole, as in details, the balances are then equalin such a concentrated brine containing about 0.5 milliized and the internal and external outputs relating to the normality of Ca ions, the solubility of the S0 is about concentrated circuit are settled. These outputs are shown 18 millinormalities, as hereinabove indicated. on FIGURE 2 whereon the partial balances may be read However, the supersaturation is lower than in vat T easily. and, despite a longer contact duration (15 minutes in- The total independence of the concentration circuit stead of 6), the dolomite contamination is not noticeable. relative to the diluted circuit (which receives brine and On the other hand, the dolomite transferred from partially converted dolomite from the former but sends converter C to converter D as indicated by line 18 leaves back nothing to it) appears clearly on FIGURE 2, and the concentrated circuit where it has finally 1031; 295+ the main point is the ability in said concentrated circuit 150:445 millinormalities of Ca, that is, 445/ 775 =57% to extract, from the dolomite utilized, all the Ca ions necof its initial content. essary:

In compensation, is has gained 300+150=450 milli. (a) To satisfy the conversion of magnesium sulphate liti f Mg, that i 450/68()=66% f it i iti l intg calcium sulphate (Equation B) stoichiometrically; content. all

Owing to its coupling with vat T and converter C, de- 70 (b) To introduce into the brines to be desulphated an sulphater S receives l+2=3 volumes respectively from excess C3012 which, y holhoionic effect, lowers the them, whereas it gives back only 2 volumes to converter 4 ions l li y "0 h a value that the soaking in C N b i 6 i fit f ki f r i i t poor i vat T may be carried out without any excessive contami- Mg. Therefore, the excess volume (1 liter) is returned, nation of dolomite by CaSO and that, after dilution of the not to vat T, but to desulphater S through pipe 20. brine from desulphater S by the washing waters at the inlet of converter D as described hereinafter, the conversion may be completed in a medium undersa-turated in C3804.

7 It is important and in accordance with the present process that this result might be obtained without any addition of make-up CaCl from the diluted circuit, for the introduction in the concentrated circuit of dilution water, in small but frequent quantities, would modify the solubility diagram of S ions, even at equal concentrations in Ca ions, and thus lower the solubility 'margin given by the dilution of a less desulphated brine 4. This change in the solubility curve of FIGURE 1, following an admission of water into the concentrated circuit, would also increase the chances of contamination during the soaking operation in vat T.

Diluted Circuit The partially converted dolomite tromconverter C is transferred into converter -D as indicated by line 18, put in suspension in exhausted brine, diluted and treated by progressive addition, in 20 minutes, of 2 volumes of diluted brine from converter D After reaction, the brine is sent to discharge through pipe 22 and the dolomite is transferred into converter D as indicated by line 24.

The composition of the discharged brine (point B of FIGURE 1) is Mg=35 millinormalities, Ca=265 millinormal-ities and SO =2O millinormalities.

It is obviously undersaturated in sulphate since in diluted brine 1:1 (point e of FIGURE 1) the S0 ions solubility is 52 millinormalities.

I-n converter D the dolomite from converter D is treated with 2 volumes of brine from converter D added progressively in 30 minutes.

The solution resulting from the reaction, for this treating time, contains about M g=100 millinormalities, Ca=205 millinorma lities and SO =20 millino-rrnalities (point F of FIGURE 1).

The brine is still undersaturated in S0,, ions which, under these conditions, have a solubility of about 60 millinormalities (point f of FIGURE 1). V

The dolomite is transferred to converter D as indicated by line 26.

In converter D it is put in suspension for 90 minutes with the diluted brine from the mixing of one volume of desulphated concentrated brine 4 irom desulphater S fed through pipe 21 and one volume of washing water coming from one volume of fresh water fed through pipe 28 to washer L This brine, after passage through washers L L and L is charged with soluble products (NaCl, CaC1 impregnating the magnesia grains as they come out of converter D where the properly so-called conversion of dolomite into magnesia has been completed.

This conversion ended in a brine containing Mg=150 millinormal-ities, Ca=l55 millinorm-ali-ties and SO =20 millinormalities (point '6 of FIGURE 1) that is still more undersaturated than the preceding ones (in fact the theoretical solubility of S0 ions is about 70 millinormalities, point g of FIGURE '1).

The three washings in washers L L and L are efliected by successive suspensions of magnesia from converter D respectively for 15, and 5 'minutes, in each washer with counterflowing water.

In order to avoid the bursting and the dispersion of the grains coming in contact with water, an MgCl content'above 1O millinormalities is maintained in each washer by means of controlled additions it necessary.

From washer L are extracted, per liter of brine uti- 'lized, '92 grams of damp cake having a moisture content of 58%, that is 38.7 grams Mg(OH) corresponding to 26.6 grams MgO.

The average decantabil-ity in the various bn'nes utilized in the process is 4 cm./minute, which is excellent.

'The undersaturation margin in S0 ions :in the diluted circuit may appear .too great (20 millinormalities com- 8 pared to 52 possibile in converter D At first sight, it would seem that the process would allow either a lesser desulphating in desulphater S (but in this case, the contaminatio n during soaking would be higher) or a reduction of 50%, for example, in the amount of washing water introduced during the diluted stage, which would involve the discharge of 1.5 volumes (instead of 2) containing about Mg=47 mi-lrlinormalities, Ca=350 millinormalities and SO =27 millinormalities, while for a Ca normality of 0.35 and in a less diluted brine the effective solubility would still be about32 mil-linormalities of S0 However, in the present example givenv .by way of illustration only and in which there are only three stages of washing, this reduced quantity of washing water, sufficient to limit the contamination of the final product by CaSO would be too small to purify the magnesia from converter D from the soluble products (NaCl, CaCl which impregnate it.

The Matter Balance of the process according to the present example, expressed in millinoi'malities, is as follows:

Magnesium:

Mg input: 8504-680 '1530 Mg eliminated in solution at discharge 70 i.e. 4.6%

Mg produced or maintained iii-solid state-.- 1460 i.e. 95.4%

that is: I

In the fines produced in vat T and converter 0 (and evacuated with the gypsum) 70 i.e. 4.6% In the fines produced in the diluted circuit (recoverable in converter D!) 60 i.e. 3.9%} 87 In the final product (calibrated)- "-1330 i.e. 86.9% 0 Ratio i MZEL=EQ 917 grainsa-g-ofines produced 1460 0 Mg y1eld= "87% Calcium:

Ca input=70+775 Ca eliminated as gypsum: 280+25. 305 i.e. 36%

Ca eliminated in converter D (CaS04:2 20) 40 i.e. 4.7%} 97 Ca in solution (OaOlz:2X(265-20)) --490 i.e. 58.2% 0a as impurities (in C3504 i.e. 0.3

2. 5 7 Ca in the product (OB-O12 undetermined: }1.1%

9-2.5) .6. 5 i.e. 0.8% SO41 S04 input 350 S04 eliminated as gypsum: 280+25 305 i.e. 87%

S04 eliminated in soluble state in converter D1:

2X20 40 i.e. 11.5%

S04 as impurities in the product -2. 5 i.e. 0.7%

$0 undetermined 2 5L8. 0.7%

The characteristics of the final product are as follows:

Ratio: CaO/MgO=9/ 1330 5 6/40 0.95% Moistur 58% I Filterability Instantaneous the scope of the following claims.

I claim: a

1. A process of converting slaked dolomite into Mg(OH) by employing an initial magnesium brine substantially saturated in Na'Cland containing, in addition to chlorides, a-substantial proportion *of sulphate, which comprises mixing with said initial brine a sufficient quantityrof a recycled concentrated brine rich in CaCl than said initial brine to thereby cause the supersaturation of calcium sulphate without lowering the 'NaCl content of the mixture and crystallize a great part of the (22180.; in the form of gypsum in a desulphating step, removing the gypsum from its mother liquor, mixing magnesium brine mother liquor from said desulphating step with slakeddolomite in a first converting step to partially convert in concentrated medium the dolomite into Mg(0H) and produce a concentrated brine 'richer in CaCl 'than said mother "liquor, utilizing the concentrated brine produced in said first converting step as the recycled brine which is mixed with said initial brine, removing the partially converted dolomite 'from said first converting step and carrying on the conversion in a second converting step .by mixing .it with magnesium-containing brine which .is more dilute than said mother liquor and is obtained by diluting mother liquor from said desulphating step with water in order to increase the solubility of the CaSO; still present in the medium and avoid its precipitation, and to obtain finally a magnesium hydroxide with a very small amount of CaSO '2. A process of converting slaked dolomite into Mg(OH) by employing an initial magnesium brine substantially saturated in NaCl and containing, in addition to chlorides, a substantial proportion of sulphate, which comprises mixing with said initial brine in a first desulphater a sufiicient quantity of a recycled concentrated brine richer in 09.61 than said initial brine to thereby cause the supersaturation of calcium sulphate without lowering the NaCl content of the mixture and crystallize a great part of the CaSO in the form of gypsum in said first desulphater, removing the gypsum from its mother liquor, mixing part of the magnesium brine mother liquor from said gypsum crystallization step with slaked dolomite in a soaking vat to partially convert in concentrated medium the dolomite into Mg(OH) and produce a concentrated brine richer in CaC1 than said magnesium brine mother liquor, transferring the partially converted dolomite to a first converter and mixing it with concentrated magnesium-containing brine richer in CaC1 than said magnesium brine mother liquor and circulating from a second desulphater through said first converter and returning to said second desulphater, feeding said second desulphater with part of the magnesium brine mother liquor from said first desulphater and with mother liquor from said soaking vat, crystallizing gypsum from the concentrated brine in said second desulphater, removing the gypsum from its mother liquor, utilizing part of the mother liquor from said second desulphater as the recycled concentrated brine which is mixed with said initial brine in said first desulphater, removing the partially converted dolomite from said first converter and carrying on the conversion in a second converting step by mixing it with magnesium-containing brine which is more dilute than said mother liquor and is obtained by diluting mother liquor from said first desu-lphater with water in order to increase the solubility of the CaSO still present in the medium and avoid its precipitation, and to obtain finally a magnesium hydroxide with a very small amount of CaSO 3. A process according to claim 2, wherein the ratio stay in desulphaters stay in converter is about 40:1.

References Cited in the file of this patent UNITED STATES PATENTS UNITED STATES PATENT OFFICE CETIFICATE OF CORRECTION Patent N00 3 051 552 August 28 1962 Andre Salol It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 2 line 7 for CaS0 ,2H O" read CaSO QZI-I O --3 column 4 line 36 for "stock" read stocks line 159 for "grain" read grains line 69 strike out "'the" second occurrence; same column 4 line 72 for "eleminated" read eliminated column 45 line 29 for "his" read this =g line 55 for "is is" read it is line 57 after "S0 insert ions same column 5 line 67 for "is" read it column 6 line 17 for feed read fed -5 line 6O for concentration" read concentrated column 8 line 1 for "possibile" read possible.

line 59 for "rich" read richer e Signed and sealed this 18th day of December 1962,

(SEAL) Attest:

ERNEST W. SWIDER DAVID L. LADD Attesting Officer Commissioner of Patents 

1. A PROCESS OF CONVERTING SLAKED DOLOMIT INTO MG(OH)2 BY EMPLOYING AN INITIAL MAGNESIUM BRINE SUBSTATIALLY SATURATED IN NAC1 AND CONTAINING, IN ADDITION TO CHLORIDES, A SUBSTANTIAL PROPORTION OF SULPHATE, WHICH COMPRISES MIXING WITH SAID INITIAL BRINE A SUFFICIENT QUANTITY OF A RECYCLED CONCENTRATED BRINE RICH IN CAC12 THAN SAID INTIAL BRINE TO THEREBY CAUSE THE SUPERSATURATION OF CALCIUM SULPHATE WITHOUT LOWERING THE NAC1 CONTENT OF THE MIXTURE AND CRYSTALLIZE A GREAT PART OF THE CASO4 IN THE FORM OF GYPSUM FROM ITS MOTHER LIQUOR, MIX STEP, REMOVING THE GYPSUM FROM ITS MOTHER LIQUOR, MIXING MAGNESIUM BRINE MOTHER LIQUOR FROM SAID DESULPHATING STEP WITH SLAKED DOLOMITE IN A FIRST CONVERTING STEP TO PARTIALLY CONVERT IN CONCENTRATED MEDIUM THE DOLOMITE INTO MG(OH)2 AND PRODUCE A CONVERTING BRINE RICHER IN CAC12 THAN SAID MOTHER LIQUOR,UTILIZING THE CONSENTRATED BRINE PRODUCTED IN SAID FIRST CONVERTING STEP AS THE RECYCLED BRINE WHICH IS MIXED WITH SAID INITIAL BRINE, REMOVING THE PARTIALLY CONVERTED DOLOMITE FROM SAID FIRST CONVERTING STEP AND CARRYING ON THE CONVERSION IN A SECOND CONVERTING STEP BY MIXING IT WITH MAGNESIUM-CONTAINING BRIN WHICH IS MORE DILUTE THAN SAID MOTHER LIQUOR AND IS OBTAINED BY DILUTING MOTHER LIQUOR FROM SAID DESULPHATING STEP WITH WATER IN ORDER TO INCREASE THE SOLUBILITY OF THE CASO4 STILL PRESENT IN THE MEDIUM AND AVOID ITS PRECIPITATION, AND TO OBTAIN FINALLY A MAGNESIUM HYDROXIDE WITH A VERY SMALL AMOUNT OF CASO4. 